1. Field of the Invention
The present invention relates to a developing apparatus, and more specifically, to a developing apparatus which controls the amount of a developer material composed of a toner and a carrier and the concentration of the toner stored in a development tank to be constant in order to supply a developer material of a constant quality to a photoreceptor through a developing roller for visualization of a latent image formed on the photoreceptor.
2. Description of the Related Art
In dry electrophotographic printers and the like, there has been widely used a developing apparatus which develops or visualizes a latent image formed on a photoreceptor by means of a developer material composed of a toner and a carrier, that is, a two-component developer material. In this kind of known developing apparatus, though the toner is consumed upon each printing operation, the carrier is not consumed but caused to circulate in the developing apparatus while being stirred. As the carrier is circulated while being stirred in this manner, a resin coating on the surface of each particle of the carrier might be peeled off, permitting the toner to be fused to the surfaces of carrier particles. As a result, an electrification function of the carrier is deteriorated, so the visualization of the latent image cannot be performed excellently. As proposals for solving this problem, there are inventions disclosed in Japanese Patent Publication No. 7-11598 and U.S. Pat. No. 4,614,165. In these inventions, it is intended to prolong the service life of a carrier in a developing apparatus substantially to that of the apparatus by replenishing the carrier little by little together with a toner. However, in these inventions, the carrier is replenished little by little at a speed determined according to a certain function, and hence the contents disclosed therein are very conceptual, so it is necessary to devise various ways and means in order to implement these inventions as concrete devices.
As one of such contrivances described above, there is an invention disclosed in Japanese Patent Publication No. 2-21591. In this invention, a carrier is gradually replenished to a developing apparatus, and a developer material overflowing from a weir of a prescribed height is collected or recovered as a discharged developer material. This method is generally called an overflow method, and there is an invention related to this method which is disclosed in U.S. Pat. No. 5,436,703. The invention of U.S. Pat. No. 5,436,703 discloses such a construction that a developer material is caused to overflow from a first chamber to a second chamber, and conveyed therefrom to a discharge port by means of a conveyor device, arranged in the second chamber. Also, Japanese Patent No. 2,891,845 and U.S. Pat. No. 5,430,532 disclose measures for coping with the case in which a developing apparatus employing an overflow method is inclined during movement thereof. Japanese Patent No. 2,891,848 discloses an invention which employs an overflow method and at the same time measures the weight of a developing apparatus and the like so as to maintain the amount of developer material in the developing apparatus at a proper level. In these developing apparatuses employing the overflow method, however, there is a tendency that an exchange or replacement ratio of the existing developer material to a freshly supplied unused developer material is varied depending upon the amount of toner consumed per sheet of paper, resulting in the unstable quality of a printed image. In order to improve these problems, complicated devices such as a weight detecting device and the like are required.
Thus, a developing apparatus without using an overflow method will be considered. As improved techniques for controlling the discharge of a developer material in such a developing apparatus, there are known inventions disclosed in Japanese Patent No. 2,574,588 and U.S. Pat. No. 5,095,338. These inventions control the discharge of the developer material by arranging a magnetic curtain at a developer material discharge port. In addition, in an invention disclosed in Japanese Patent No. 2,837,309, a shutter is disposed at a discharge port of a developing apparatus for controlling a developer material in such a manner that the developer material is prevented from being discharged from the discharge port during the time when an image forming operation is carried out. In this case, however, in order to stabilize the operation of the developing apparatus, it is necessary to detect the total amount of developer material and the amount of discharged developer material in addition to the concentration of the toner thereby to control a developer material supply means and a toner supply means, as disclosed in U.S. Pat. No. 5,548,385. Alternatively, it is necessary to detect the amount of toner consumed and perform discharge control so as to maintain the amount of developer material at a prescribed level, as disclosed in Japanese Patent Application Laid-Open No. 10-63074 or Japanese Patent Application Laid-Open No. 10-90991. Accordingly, these measures are rather complicated in construction to put into practice.
In this manner, the above-mentioned conventional developing apparatuses, whether employing an overflow method or not, are complicated in construction. Then, a proposal for simplifying the constructions of these developing apparatuses has been made in Japanese Patent No. 3,005,138. By applying the technique disclosed therein, it is possible to prolong the usable life of a developer material in a developing apparatus by supplying a fresh developer material from a developer material replenishment tank to the developing apparatus little by little, and at the same time by discharging the developer material in the developing apparatus from a discharge port thereby to gradually refresh the developer material in the developing apparatus. In this technique, however, it is necessary to replenish and discharge the developer material very little by very little at the same time, and if otherwise, the developer material will fill up a discharge tank in a short time. In addition, it is not convenient to use because it is necessary to exchange the replenishment tank and the discharge tank, respectively, each time they are emptied or filled up. The cause of this is a one-way flow of the developer material in a direction from the replenishment tank to the discharge tank.
The present invention is intended to solve the above-mentioned problems, and has for its object to provide a developing apparatus which is simple in structure, and is capable of preventing deterioration of a developer material in the developing apparatus, by detachably mounting a developer material storage vessel with a fresh developer material stored therein on a development tank so that the developer material gradually discharged from the development tank is received in the developer material storage vessel and mixed with the developer material thus far stored in the developer material storage vessel, then an amount of developer material thus mixed equal to the amount of developer material discharged to the developer material storage vessel being returned to the developing apparatus.
To solve the above-mentioned problems, the present invention resides in a developing apparatus for supplying a developer material composed of a toner and a carrier to a photoreceptor to visualize a latent image formed on the photoreceptor. The apparatus includes: a development tank for storing the toner and the carrier; a development roller for supplying the toner and the carrier in the development tank to the photoreceptor; and developer material refreshing means for mechanically forcing the development tank to supply and receive the toner and the carrier, which together constitute the developer material, so as to prevent changes in the amount of the developer material and in the concentration of the toner in the development tank.
According to the above construction, the service life of the developer material can be prolonged by forcedly refreshing the developer material in the development tank little by little by forcedly exchanging the developer material in the development tank, which has reached a certain fixed height, under the action of the developer material refreshing means without depending on an overflow of the developer material in the development tank alone as in the above-mentioned conventional apparatuses.
In addition, in the present invention, the developer material refreshing means includes: toner concentration adjusting means for supplying a toner to the developer material stored in the development tank thereby to set the concentration of the toner therein to a target toner concentration; a developer material storage vessel detachably mounted on the development tank for storing a developer material of the target toner concentration; and a developer material discharging and receiving mechanism for mixing the developer material stored in the development tank with the developer material stored in the developer material storage tank a prescribed amount by a prescribed amount, and circulating them into the development tank without giving a change equal to or greater than a predetermined amount to the amount of developer material stored in the development tank.
Moreover, in the present invention, the developer material refreshing means includes: discharging and conveying means for discharging and conveying the developer material in the development tank a prescribed proper amount by a prescribed proper amount; developer material replenishment means for storing a developer material of a target toner concentration and supplying the developer material in such a manner that the amount of developer material stored in the development tank becomes constant; and a high concentration developer material storage part detachably mounted on the developer material replenishment means for storing a high concentration developer material of a toner concentration higher than the target toner concentration, receiving, the developer material discharged from the discharging and conveying means to mix it with the high concentration developer material, and delivering the mixed developer material to the developer material replenishment means when the toner concentration of the mixed developer material has reached the target toner concentration.
Further, in the present invention, the developer material refreshing means includes: discharging and conveying means for discharging and conveying the developer material in the development tank a prescribed proper amount by a prescribed proper amount; developer material replenishment means for storing a developer material of a target toner concentration and supplying the developer material in such a manner that the amount of developer material stored in the development tank becomes constant; toner replenishment means for replenishing the amount of the toner; and developer material stirring means for receiving the developer material from the discharging and conveying means and the toner from the toner replenishment means to mix them with each other to produce a mixed developer material, and delivering the mixed developer material to the developer material replenishment means when the toner concentration of the mixed developer material has reached the target toner concentration. The developer material replenishment means is removable from the development tank and the developer material stirring means connected therewith.
Furthermore, in the present invention, the developer material refreshing means includes: discharging and conveying means for discharging and conveying the developer material in the development tank a prescribed proper amount by a prescribed proper amount; developer material replenishment means for storing a developer material of a target toner concentration and supplying the developer material in such a manner that the amount of developer material stored in the development tank becomes constant; a high concentration developer material storage part for storing a high concentration developer, material of a toner concentration higher than the target toner concentration; developer material conveying means connected with the high concentration developer material storage part; and developer material stirring means for mixing the developer material discharged from the discharging and conveying means and the high concentration developer material in the high concentration developer material storage part received from the developer material conveying means to produce a mixed developer material, and delivering the mixed developer material to the developer material replenishment means when the toner concentration of the mixed developer material has reached the target toner concentration. When the high concentration developer material storage part is emptied, the developer material conveying means conveys the developer material in a reverse direction from the developer material stirring means the high concentration developer material storage part so that an amount of carrier stored in the high concentration developer material storage part at the time of initialization is maintained in the high concentration developer material storage part so as to make it possible to replace the high concentration developer material storage part with a new one.
Further, the present invention resides in a developing apparatus in which a predetermined amount of developer material composed of a toner and a carrier stored in a development tank is stirred by stirring means and supplied to a latent image, which is formed on a photoreceptor in accordance with an electrophotographic method, by a development roller arranged in the development tank to visualize the latent image, a concentration of a toner consumed in the development tank being detected by a toner concentration sensor whereby the toner in the toner storage tank is supplied to the development tank so as to maintain the toner concentration therein at a constant value. The developing apparatus includes: developer material discharging means for mechanically discharging the developer material from the development tank; developer material receiving means for receiving the developer material into the development tank; developer material storage means detachably mounted on the developer material discharging means and the developer material receiving means for storing in advance the same developer material as that stored in the development tank at the time of initialization; and control means for driving the developer material discharging means to discharge a predetermined amount of developer material from the development tank to the developer material storage means so as to mix the developer material discharged from the development tank and the developer material already stored in the developer material storage means with each other, the control means further driving the developer material receiving means in such a manner that the development tank is made to receive from the developer material storage means an amount of mixed developer material corresponding to an amount of developer material discharged from the development tank.
Still further, in the present invention, the developer material, which is caused to circulate through the developer material storage means by the control means, is a developer material whose height in the development tank becomes equal to or higher than a predetermined height level.
Besides, in the present invention, the conveyance capacity of the developer material receiving means for conveying the developer material is greater than that of the developer material discharging means.
In addition, in the present invention, a discharge port, through which the developer material discharging means discharges the developer material from the development tank, and a receiving port, through which the developer material receiving means makes the developer material received in the development tank, are set at locations opposing to each other in such a manner that a distance between the discharge port and the receiving port in the development tank is longer than a direct distance therebetween in a straight line.
Moreover, in the present invention, the control means circulates the developer material through the developer material storage means when image formation is not performed.
Further, in the present invention, the developer material storage means is integral with the toner storage tank.